Influence of dietary zinc on growth, zinc bioaccumulation and expression of genes involved in antioxidant and innate immune in juvenile mud crabs (Scylla paramamosain)

Abstract

The aim of present study was to investigate the effects of dietary Zn level on growth performance, Zn bioaccumulation, antioxidant capacity and innate immunity in juvenile mud crab (Scylla paramamosain). Six semi-purified diets were formulated to contain dietary Zn levels of 44.5, 56.9, 68.5, 97.3, 155.6 or 254.7 mg·kg-1, respectively. Dietary Zn level significantly influenced percent weight gain (PWG), with highest observed in crab fed the diet containing 97.3 mg·kg-1 Zn. Tissue Zn concentrations significantly increased as dietary Zn levels increased from 44.5 to 254.7 mg·kg-1. Retention of Zn in hepatopancreas increased with dietary Zn levels up to 68.5 mg·kg-1 and then significantly decreased. Moreover, inadequate dietary Zn (44.5 and 56.9 mg·kg-1) reduced anti-oxidation markers including total superoxide dismutase and copper/zinc superoxide dismutase activities and total anti-oxidant level. Crabs fed the diet with 44.5 mg·kg-1 Zn also showed significantly lower expression of genes involved in antioxidant status, such as Cu/Zn sod, glutathione peroxidase, catalase and thioredoxin than those fed diets containing 68.5 and 97.3 mg·kg-1 Zn. Highest activities of phenoloxidase and alkaline phosphatase were recorded in crab fed the diets containing 68.5 and 97.3 mg·kg-1 Zn. Expression levels of prophenoloxidase and toll-like receptor 2 were higher in crab fed the 97.3 mg·kg-1 Zn diet compared to crab fed the other diets. Based on PWG alone, the optimal dietary Zn level was estimated to be 82.9 mg·kg-1, with 68.5 to 97.3 mg·kg-1 recommended for maintaining optimal Zn bioaccumulation, oxidation resistance and innate immune response of juvenile mud crab.